IR-780 Iodide: Properties, Applications & Protocols

IR-780 iodide is a lipophilic, near-infrared heptamethine cyanine fluorescent dye valued in biomedical research for its strong NIR absorption, mitochondria-targeting behavior, and dual utility in photodynamic and photothermal therapy applications.

Chemical Class

Heptamethine cyanine dye (iodide salt)

Absorption Maximum

~780 nm (near-infrared region)

Emission Maximum

~820 nm (near-infrared region)

Primary Subcellular Target

Mitochondria (driven by membrane potential)

Solubility

Soluble in DMSO and ethanol; poorly soluble in aqueous buffers

Key Applications

NIR fluorescence imaging, PDT, PTT, tumor targeting, nanoparticle formulation

Aladdin SKU

I302749

What Is IR-780 Iodide?

IR-780 iodide is a synthetic, lipophilic heptamethine cyanine dye with an iodide counterion. Its conjugated polymethine backbone confers strong light absorption in the near-infrared (NIR) window (~650–900 nm), a spectral region of particular interest in biomedical optics because tissue scattering and autofluorescence are minimized. The compound is structurally related to indocyanine green (ICG) but offers improved photostability and cell-membrane permeability, making it attractive for both in vitro and in vivo studies.

Because of its positive charge and high lipophilicity, IR-780 iodide accumulates preferentially in mitochondria of mammalian cells, driven by the large negative mitochondrial membrane potential (Δψm). This organelle-selective localization forms the basis of its widespread use as a mitochondria-targeting fluorescent probe and as a carrier moiety in mitochondria-directed drug delivery systems.

Physicochemical Properties and Stability

IR-780 iodide appears as a dark green to blue-green crystalline solid. The compound is readily soluble in polar aprotic solvents such as dimethyl sulfoxide (DMSO) and in alcohols (e.g., ethanol), but its solubility in aqueous physiological buffers is limited due to its hydrophobic heptamethine core. Stock solutions are typically prepared in DMSO at concentrations of 1–10 mM and stored protected from light at −20 °C to minimize photodegradation.

Like most cyanine dyes, IR-780 iodide is susceptible to photobleaching upon prolonged exposure to ambient light or intense laser irradiation. Researchers should handle the compound under subdued or red-filtered lighting, prepare working solutions freshly before each experiment, and avoid repeated freeze-thaw cycles. When encapsulated in nanoparticle carriers (e.g., PLGA, lipid nanoparticles, or polymeric micelles), photostability is often significantly improved.

The dye's NIR absorption maximum is approximately 780 nm, and its fluorescence emission peak falls near 820 nm, placing both values within the first biological window (650–950 nm). Molar absorptivity is high (reported values in the literature typically exceed 10⁴ L mol^-1 cm^-1), supporting sensitive detection at low dye concentrations.

Research Applications

NIR Fluorescence Imaging: IR-780 iodide is used as a contrast agent for in vivo NIR fluorescence imaging of tumors, lymph nodes, and vascular structures. Its preferential accumulation in tumor mitochondria—attributed partly to the elevated Δψm of cancer cells—enables passive tumor targeting. When formulated into nanoparticles, the enhanced permeability and retention (EPR) effect further concentrates the dye at tumor sites.

Photodynamic Therapy (PDT): Under NIR laser irradiation, IR-780 iodide can generate reactive oxygen species (ROS), including singlet oxygen, enabling it to function as a photosensitizer for PDT. This property has been exploited in cancer cell-killing experiments both in vitro and in vivo. The NIR excitation wavelength used for PDT provides deeper tissue penetration compared with UV or visible-range photosensitizers.

Photothermal Therapy (PTT): IR-780 iodide can convert absorbed NIR photons into heat through non-radiative relaxation pathways, generating localized hyperthermia that damages tumor cells. When loaded into nanocarriers, it has been used for combined PTT/PDT approaches, demonstrating synergistic anti-tumor effects in preclinical models.

Drug Delivery and Theranostics: The dye's fluorescence enables real-time tracking of nanoparticle biodistribution, while its PDT/PTT activity provides a therapeutic function—a combination that exemplifies the theranostic (therapy + diagnostics) paradigm. IR-780-loaded nanoparticles co-delivering chemotherapeutic agents (e.g., doxorubicin or paclitaxel) have been investigated for synergistic anti-cancer activity.

Mitochondria Research: As a mitochondria-selective dye, IR-780 iodide serves as a tool for assessing mitochondrial membrane potential changes, mitochondrial dynamics studies, and as a targeting ligand to direct payloads (drugs, nucleic acids) to mitochondria.

Handling, Preparation, and Safety Guidelines

Stock Solution Preparation: Dissolve IR-780 iodide in anhydrous DMSO to prepare a concentrated stock solution (1–10 mM). Vortex briefly and sonicate if needed to ensure complete dissolution. Filter-sterilize (0.22 µm) if the solution is intended for cell culture or animal studies. Aliquot into single-use volumes to avoid repeated freeze-thaw cycles, and store at −20 °C in amber vials or wrapped in aluminum foil.

Working Solution Preparation: Dilute the DMSO stock with the appropriate aqueous medium (cell culture medium, PBS, etc.) to the desired working concentration immediately before use. Keep the final DMSO content below 0.1% (v/v) for cell-based assays to minimize solvent cytotoxicity. Note that precipitation may occur at high aqueous dilution ratios; nanoparticle encapsulation or the use of co-solvents can mitigate this.

Light and Temperature Sensitivity: Always work under subdued lighting. Completed experiments and remaining solutions should be wrapped in foil and stored at −20 °C. Do not leave solutions exposed on the bench for extended periods.

Safety: IR-780 iodide is an experimental research reagent and should be handled in accordance with standard laboratory safety practices. Wear appropriate personal protective equipment (PPE) including gloves, lab coat, and eye protection. As with any iodide-containing compound, avoid inhalation of dust or aerosols. Consult the Safety Data Sheet (SDS) provided by Aladdin Scientific for complete hazard, first-aid, and disposal information before use.

Ordering Information and Formulation Tips

IR-780 iodide is available from Aladdin Scientific under SKU I302749. The compound is offered as a solid powder. Upon receipt, briefly centrifuge the vial before opening to consolidate any material that may have settled on the cap or walls during shipping.

Nanoparticle Encapsulation: For researchers requiring aqueous-compatible formulations with improved stability, encapsulation of IR-780 iodide into biodegradable polymer nanoparticles (e.g., PLGA), lipid nanoparticles, or amphiphilic block copolymer micelles is well established in the literature. Encapsulation typically improves photostability, aqueous dispersibility, and circulation half-life in vivo. Nanoprecipitation and emulsion-solvent evaporation are commonly reported preparation methods.

Quality Verification: Users are encouraged to verify compound identity and purity by UV-Vis spectrophotometry (confirm absorption maximum near 780 nm in DMSO or ethanol) and, where available, by HPLC or mass spectrometry before use in critical experiments. Contact Aladdin Scientific customer support for Certificate of Analysis (CoA) documentation.

Frequently asked questions

What solvents are recommended for dissolving IR-780 iodide?

IR-780 iodide dissolves readily in DMSO and ethanol, which are the most commonly used solvents for preparing stock solutions. It has poor solubility in purely aqueous buffers; therefore, working solutions should be prepared by diluting the organic stock into aqueous media immediately before use, keeping the organic solvent content as low as possible (typically ≤0.1% v/v for cell assays).

Why does IR-780 iodide accumulate in mitochondria?

The preferential mitochondrial accumulation of IR-780 iodide is driven by its cationic charge and high lipophilicity. Mitochondria maintain a large negative membrane potential (Δψm, typically −180 to −200 mV in healthy cells), which electrostatically attracts and retains lipophilic cations within the organelle. Cancer cells often exhibit a more hyperpolarized or otherwise altered Δψm, which can further enhance selective accumulation in tumor mitochondria.

Can IR-780 iodide be used for both PDT and PTT simultaneously?

Yes. IR-780 iodide possesses both photosensitizing (ROS-generating) and photothermal conversion properties upon NIR laser irradiation, enabling its use as a dual PDT/PTT agent. Numerous preclinical studies have exploited this dual functionality—particularly when the dye is encapsulated in nanoparticles—to achieve synergistic anti-tumor effects. The ratio of PDT to PTT activity can be influenced by dye concentration, laser power density, and the local environment (e.g., oxygen availability for PDT).

How should IR-780 iodide be stored to maintain stability?

Store IR-780 iodide as a solid at −20 °C in a tightly sealed vial, protected from light. DMSO stock solutions should also be stored at −20 °C in amber vials or aluminum-foil-wrapped tubes, and aliquoted to avoid repeated freeze-thaw cycles. Avoid exposure to moisture, heat, and direct light at all times to minimize degradation.

What excitation and emission wavelengths should be used for imaging with IR-780 iodide?

IR-780 iodide has an absorption maximum at approximately 780 nm and an emission maximum at approximately 820 nm. For fluorescence imaging experiments, an excitation laser or light source near 780 nm and an emission filter centered around 820 nm (or a long-pass filter >800 nm) are appropriate. Confirm optimal settings empirically using your specific instrument, as slight spectral shifts can occur depending on solvent and local environment.

References

1. Shi C, et al. A research on the positive correlation between the uptake of IR-780 iodide and the membrane potential in various tumor cell lines. Journal of Fluorescence. 2013.
2. Wang Y, et al. IR-780 dye encapsulated in polymeric nanoparticles for in vivo near-infrared imaging and photothermal/photodynamic therapy. Biomaterials. (year not confirmed in source).
3. Luo S, et al. Heptamethine cyanine dyes: synthesis, properties, and biological applications. Chemical Reviews. (year not confirmed in source).

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